The present invention relates to apparatus and method for altering the relative rotational phase of two members otherwise keyed to rotate together in phase and more particularly to a dual-acting phasing apparatus and method for shifting concentric camshafts of a camshaft assembly.
As used herein, a single-acting phasing mechanism enables the period of rotation of one rotating member to be altered relative to the period of rotation of a second rotating member. Examples of single-acting phasing mechanisms include the electro-mechanical unit described in U.S. Pat. No. 4,770,060 issued to Elrod et al, which is owned by the assignee of the caption application and is hereby incorporated herein by this reference. One embodiment of this phaser uses Harmonic Drive.TM. brand gearing such as described in U.S. Pat. Nos. 2,906,143 and 2,959,065 and available from the Harmonic Drive Division of Emhart Machinery Group, Wakefield, Mass. Other single-acting phasing mechanisms are described in U.S. Pat. No. 4,754,727 to Hampton, U.S. Pat. No. 4,494,495 to Nakamura et al, U.S. Pat. No. 5,121,717 to Simko et al, and U.S. Pat. No. 5,117,784 to Schechter et al. The latter also describes a mechanism for phase shifting a camshaft rotating along the same axis as the phasing mechanism relative to a nonconcentric camshaft located along a different but parallel axis of rotation. The foregoing six patents are hereby incorporated into this application by this reference.
As shown in FIGS. 7, 10 and 12 of U.S. Pat. Nos. 4,771,742 and 4,917,058 to Nelson et al, which are owned by the assignee of the caption application and are hereby incorporated herein by this reference, apparatus and method for variable valve timing has included the use of two single-acting camlobe phasing mechanisms, one mounted on each opposite end of the concentric camshaft assembly for rotating the concentric shafts independently of one another. In this configuration, each of the phasing mechanisms can operate independently of the other phasing mechanism. However, configurations of some engine compartments may preclude using a single-acting phaser on each end of the shaft. Moreover, depending on the particular circumstances, it is desirable either to have mutually dependent operation of the phasing of two rotating members or independent phasing of each of two concentric camshafts.